UV-curing encapsulation compounds are predominantly used in mass production, owing to the fast curing time. Approximately 90% of all chip modules for smart cards are encapsulated with encapsulation compounds such as these. The encapsulation compounds must be permeable to light, in order to allow them to cure all the way through. Alternatively, thermally curing encapsulation compounds are used. These need not be permeable to light and are often colored black. However, thermal curing has the disadvantage that it is too slow for mass production with a curing time of up to 3 minutes, and forms a relatively brittle encapsulation compound in the cured state. In comparison to this, UV-curing encapsulation compounds require only 30 to 40 seconds for curing, and thus satisfy the speed requirements of chip module manufacturers.
Since smart cards are used for identification and authentication in the field of banks and for access monitoring, the security of the data stored in the smart card is subject to very stringent requirements. If it is possible to read secret data from a smart card, or to manipulate it, then, in the worst case, it may be necessary for the system operator to shut down the system, to block all cards and to issue new cards which are immune to attack. The financial damage and the loss of confidence would be immense.
Attacks are made on weaknesses of smart cards at all levels. An attack at the physical level may, for example, make use of the free access of light to the chip in the chip module. It would thus be possible in the visible spectrum at wavelengths from 400 nm to 700 nm to read secret keys with the aid of an optical microscope. Thermal measurements in the infrared range from 700 to 2500 nm could be used to determine which parts of the chip circuit are heated, that is to say are currently operating. In this way, for example, it would be possible to determine the procedure sequence in an algorithm. Apart from optical analysis, free access of light to the chip also allows the chip to be deliberately disturbed, and a subsequent malfunction to be made use of. This could be done, for example, by irradiation of the chip with photons, which release electrons from the semiconductor lattice, and could thus deliberately lead to a change in the memory content or manipulation of data.
Optical analysis and influencing the chip by irradiation in the wavelength range from 200 nm to 2500 nm can be avoided by the use of light-impermeable encapsulation compounds, although these are not suitable for mass production of smart cards, owing to the slow curing time and their brittle nature.